1. Field of the Invention
The present invention pertains to circuitry for driving light emitting devices and pertains particularly to the low current drive of organic light emitting diodes.
2. Related Information
The organic light emitting diode (OLED) technology provides a low current emissive display technology. However, a large array of OLEDs contains a large amount of capacitance. This capacitance must be charged and discharged during multiplexed operation.
An equivalent circuit for an OLED pixel is a capacitor in parallel with the emitting diode. Typically the anodes of each OLED is driven by a current source since the pixel Vf may vary for individual OLEDs across an OLED array.
A typical implementation of circuitry which drives an array of OLEDs is using current sources to drive a column line for each column of an OLED array. The anode of each OLED is connected to a corresponding column line. The cathodes of each OLED is connected to a corresponding row line of the OLED matrix. Each row line has a switch. The switches enable one row at a time.
For background information on circuitry for driving OLEDs, see for example, U.S. Pat. No. 5,828,181 issued to Yohiyuki Okuda on Oct. 27, 1998 for DRIVING CIRCUIT FOR AN ORGANIC ELECTROLUMINESCENT ELEMENT USED IN A DISPLAY.